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sciencehabit writes: Planetary scientists have found an asteroid spinning too fast for its own good. The object, known as 1950 DA, whips around every 2.1 hours, which means that rocks on its surface should fly off into space. What's keeping the remaining small rocks and dust on the surface? The researchers suggest van der Waals forces, weak forces caused by the attraction of polar molecules, which have slightly different charges on different sides of the molecule. For example, water molecules exhibit surface tension because of van der Waals forces, because the negative charge of one water molecule's oxygen atom is attracted to nearby water molecules' hydrogen atoms, which have a positive charge at their surfaces. Similar attractions could be occurring between molecules on the surfaces of different pieces of dust and rock. Such forces would be comparable to those that caused lunar dust to stick to astronauts' space suits.

That thought was the very first thing that crossed my mind.I mean the only super dense stuff that I've read about is ultra-dense deuterium( It's in the range of 100+ tons/ cm3 ) but it's only produced in really small quantities

I would really enjoy knowing if something ultra dense is produced, and how does it effect gravity. I think that would be a fun project

So, since it has been established that the asteroid in question is pretty much a chunk of metal, and the rate of rotation would be fast enough to dislodge independent pieces of material, the obvious answer is "the rubble already flew off, this is a big hunk of nickel-iron." After doing that bit of research, I don't care what is in the summary or the article behind this story, they'd better show up with a good argument that this piece of metal has any rubble clinging to it before I will waste the effort considering other explanations.

The article doesn't explain why the idea of this particular body being one mass instead of a rubble pile has been dismissed. Is there a good one?

Asteroids are believed to be aggregations of relatively loosely bound matter. They have likely experienced some local melting due to collisions, but it is very unlikely that they ever were entirely melted into a single mass. As such, they are quite peculiar bodies, much less akin to a mountain than a pile of rubble, and they likely aren't even all that close to a pile of rubble because the individual components they are made from were never part of a larger, more coherent body.

What's keeping a piece of rock that used to be molten lava together? Crystalline ionic attractive forces. Van der Waals forces would not be strong enough to keep such an asteroid together, and that's proof that the whole thing flew off as one piece from some supernova explosion. Maybe that's the idea of catching these asteroids with spacecraft - see what stuff looks like coming straight out of a supernova, as opposed to stuff that has been impact pounded into the Moon's surface, or glowing-hot shooting star thermally remelted on the Earth's surface. The stuff that lands on Earth is mostly remnants of shooting stars that did not completely combust, but there might be some meteorite rocks that were traveling with speed close to that of Earth on rendezvous, and only attained terminal velocity in the atmosphere that's not fast enough to melt them. So some meteorites that land on the Earth could be very similar to a captured asteroid out there, and a lot cheaper. Another aspect of capturing an asteroid is practice: for when we have to capture stuff in space to build space stations out of them. Space is very very empty, huge distances of vacuum with very little stuff sprinkled here and there. Any stuff, any matter, is worth gold in outer space, especially away from a gravity well like Earth or Jupiter, but the Moon is better.

Regardless, it's quite an interesting conundrum. I suppose it's possible that high-energy collisions melted the material which would become the asteroid and it coalesced into solid chunk(s) which are unaffected by the high rotation rate.

You're still not correct, but I should have said "plane of the ecliptic," (or "ecliptic plane") rather than just "ecliptic." My apologies for any confusion. However, "elliptic plane" refers to any planar ellipsoid surface, while "plane of the ecliptic" specifically refers to the region in which the sun and the vast majority of other matter in our solar system resides.

That region is a three-dimensional ellipsoid (an example of a planar surface in the shape of an ellipse), is correctly referred to as the " [universetoday.com]

It might be in the epileptic plane (so its shaken and not stirred). I dont think anyone has an electric plane yet. Airbus might be considered an eclectic plane. Or perhaps you meant the ecliptic plane?

TFS says that vdW interactions are interactions between polar molecules... that's absolutely false! The reason water has a high surface tension is due to hydrogen bonding, which is a combination of polar interactions and charge transfer. The reason that polar molecules attract is entirely due to electrostatic reasons... electric dipoles aligning causing favorable interactions. Van der Waals interactions are when NON-polar molecules spontaneously polarize one another to form instantaneous dipoles, which attract electrostatically. The key here is that vdW attractions occur even in molecules that do not have any static dipole... the dipole-dipole interactions are dynamic and fluctuating. One of the hallmarks of vdW interactions are their asymptotic behavior. Charge-charge interactions die off as r^-1. Dipole-dipole interactions die off as r^-3. vdW interactions die off as r^-6.

You're lucky Slashdot doesn't have a "-1: Basic Grasp of Relevant Concepts", because I'm sure you'd be modbombed by it.

Maybe I'm just old, but I'm really sick of seeing articles, interviews, etc. where the "expert", often times an actual degree-wielding scientist, gets fundamental concepts completely wrong. Every time I hear someone explain lift with "air on the top of the wing has to move faster, so... lift!" I want to defecate into their open mouths.

I'm not sure I know what you mean. Where have I failed to grasp the relevant concepts? I'm merely criticizing the mistaken impression that TFS (which is apparently lifted directly from TFA) gives about what vdW forces are.

I'm not sure I know what you mean. Where have I failed to grasp the relevant concepts? I'm merely criticizing the mistaken impression that TFS (which is apparently lifted directly from TFA) gives about what vdW forces are.

I'm saying you do exhibit a basic grasp of relevant concepts, that on Slashdot people who are correct usually get shat upon, and that the "experts" in TFA often don't have a basic grasp of the relevant concepts, as your post illustrates.

Every time I hear someone explain lift with "air on the top of the wing has to move faster, so... lift!" I want to...

There's nothing at all wrong with that explanation. It is neither better nor worse than any other explanation that is less than a full solution to the Navier-Stokes equation, and it provides a naive and surprisingly practical guide to interacting with airfoils, which the vorticity explanation, for example, does not.

Air doesn't have to "move faster". Viewing the profile of a wing and using it as a fixed reference point, the air on top doesn't have to move faster in the horizontal plane at all, it just has to be deflected. Air moving at a velocity (or a relatively faster one) doesn't create a force. Air moving faster than other air doesn't create lift.What creates lift is the deflection of air. This is achieved by the angle of attack of the wings. When air has to change direction there's acceleration, and thus forc

Aren't vdW interactions any non-ionic, non-covalent interactions, including dipole-dipole (though I wouldn't include hydrogen bonding, as they are partly covalent)? With London forces, that falls off with r^-6 being an example of vdW interactions?'

Such forces would be comparable to those that caused lunar dust to stick to astronauts' space suits.

Ohh stop it! Now after so many years we should just admit the dust was sticking because they were too hasty starting to use the new set in the area 51 studio's and the black paint hadn't yet fully dried.

While that relates to the orbital speed [wikipedia.org] calculated for the mass and radius of 0.4642m/s, it is far less than the escape velocity [wikipedia.org] of 0.6565m/s [google.com]. So how far out would it go?

The numbers are so small that if you take the speed they are moving of 0.5157m/s tangental to the surf

Maybe it's got a quantum black hole at it's center, and it's just big enough to provide sufficient gravity to prevent debris on the surface from departing, but small enough that it's not rapidly consuming the asteroid yet?